Python returning none instead of string output

Question

I make some code about shrinking string in recursive function.

when input string is over it returns output.

it shows right thing in function but it returns None, instead of answer

def rec_encyption(input, i, cnt, output):
    if i + 1 == len(input):
        print(output)
        return output
    elif input[i] == input[i + 1]:
        rec_encyption(input, i + 1, cnt + 1, output)
    else:
        output = output + input[i] + str(cnt)
        rec_encyption(input, i + 1, 1, output)

def do_rec_encyption(input):
    n = rec_encyption(input + " ", 0, 1, "")
    print(n)
    return n

print(do_rec_encyption("aaabbcccccca"))

I run this code in VSCode and the result is this:

a3b2c6a1

None

which means rec_encyption return None, instead of 'output'

I can't find why and how to fix this problem

score 1 · Answer 1 · answered Dec 01 '19 at 15:11

use return in else

def rec_encyption(input, i, cnt, output):
    if i + 1 == len(input):
        print(output)
        return output
    elif input[i] == input[i + 1]:
        return rec_encyption(input, i + 1, cnt + 1, output)
    else:
        output = output + input[i] + str(cnt)
        return rec_encyption(input, i + 1, 1, output)

Python returning none instead of string output

1 Answers1